The present invention relates to a mass spectrometer and a method of mass spectrometry that use Electron Capture Dissociation (“ECD”) or Electron Transfer Dissociation (“ETD”) to fragment ions.
Atmospheric pressure Electron Capture Dissociation (“AP-ECD”) mass spectrometers are known wherein analyte ions generated by an Electrospray (“ESI”) ion source interact with photoelectrons. A UV lamp is arranged to emit UV photons which are absorbed by gas, causing the release of photoelectrons. Analyte ions interact with the photoelectrons causing the analyte ions to fragment at atmospheric pressure.
A problem with known AP-ECD mass spectrometers is that it is difficult to associate parent ions with their fragment ions. Alternative techniques tend to associate parent ions with their fragment ions by selecting a single type of parent ion at a given time and fragmenting this single parent ion to determine its fragment ions. Although this technique has a relatively low duty cycle, since other parent ions are discarded whilst the single parent ion is selected, it provides a relatively simple method of associating parent ions with their fragment ions. However, in AP-ECD techniques there is no means of selecting a specific parent ion for fragmentation because the parent ions are arranged in a high pressure region and so the conventional techniques for ion selection cannot be used. Furthermore, once the analyte ions have been fragmented there is no known means of associating the fragment ions to their precursor ions. When a sample being analysed contains a mixture of analytes, this can result in complex fragment ion spectra which include photo-ionised solvent background peaks, dopant ions and their derivatives, un-reacted parent ions, as well as mixtures of fragment ions and charge-reduced species from different parent ions. Accordingly, assigning parent ions to their fragment ions remains a complex problem in AP-ECD techniques and this complexity limits the analytical utility and commercial acceptance of the technique.
It is desired to provide an improved mass spectrometer and method of mass spectrometry. Preferably, it is desired to provide a mass spectrometer and method of mass spectrometry that are able to fragment parent ions via ECD or ETD at atmospheric pressure and then associate the resulting fragment ions with their parent ions.